"SyntaxError: non-default argument follows default argument" confuses

[Bluenix2]

BPO	47054
Nosy	@terryjreedy, @gpshead, @vedgar, @pablogsal, @Bluenix2
PRs	bpo-47054: Call params parameters not arguments in SyntaxErrors. #32014

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/gpshead'
closed_at = None
created_at = <Date 2022-03-18.01:17:42.872>
labels = ['interpreter-core', 'type-bug', '3.10', '3.11']
title = '"SyntaxError: non-default argument follows default argument" confuses'
updated_at = <Date 2022-03-20.21:18:26.112>
user = 'https://github.com/Bluenix2'

bugs.python.org fields:

activity = <Date 2022-03-20.21:18:26.112>
actor = 'gregory.p.smith'
assignee = 'gregory.p.smith'
closed = False
closed_date = None
closer = None
components = ['Interpreter Core']
creation = <Date 2022-03-18.01:17:42.872>
creator = 'bluenix'
dependencies = []
files = []
hgrepos = []
issue_num = 47054
keywords = ['patch']
message_count = 4.0
messages = ['415463', '415469', '415526', '415530']
nosy_count = 5.0
nosy_names = ['terry.reedy', 'gregory.p.smith', 'veky', 'pablogsal', 'bluenix']
pr_nums = ['32014']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue47054'
versions = ['Python 3.10', 'Python 3.11']

[Bluenix2]

Running the code below will produce a SyntaxError with the message: "non-default argument follows default argument".

    def test(a=None, b):
        return b if a is None else a

The issue is that a and b aren't arguments, rather, they are parameters. The error message should be changed to: "non-default parameter follows default parameter".

This change appears simple enough and although it is not something I've found to be troublesome, it will help users to use correct keywords (arguments vs. parameters) when searching on the internet.

[vedgar]

The problem is more subtle. The thing is, "default parameter" doesn't make sense in this context. Yes, a and b are parameter, but a is not "default parameter" in any sensible way. It is _None_ which is the default argument for parameter a, while parameter b has no default argument. In other words, if the function weren't called with a first argument, the default argument would be used.

So, the fix should be a bit more complicated. Maybe, "a parameter without a default follows a parameter with a default"?

[Bluenix2]

Yes I agree, that would be the best.

[terryjreedy]

Current message same in 3.11 and 3.9, but I am not sure about backporting to old parser. However merges a change, if any, can decide.